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ON THE NATUEE OF THE EFFECT OF THE SUN-SPOT 

 FEEQUENCY ON THE VAEIATION OF THE MAG- 

 NETIC ELEMENTS AT THE CAPE OF GOOD HOPE. 



By G. H. H. Fincham, M.A. 



(Eead March 28, 1906.) 



§ 1. The relationship existing between the Sun-spot Frequency and 

 the variation of the various elements of Terrestrial Magnetism has of 

 late been much discussed. So far, however, no results for the Cape 

 of Good Hope have been published ; the following is an account of 

 some of these and of how they have been obtained. The observa- 

 tions upon which this investigation is based are those taken by a 

 detachment of the Eoyal Artillery during the period 1842-1846, 

 both inclusive, and published by Sabine in a series of volumes 

 entitled " Magnetical and Meteorological Observations," a copy of 

 which is to be found at the Eoyal Observatory (Cape). 



§ 2. Declination. 



Sabine gives a table of figures representing in Scale Divisions the 

 mean hourly position of the magnet of the Declinometer for the 

 period 1842-1846. Wolf's formula for associating magnetic quan- 

 tities with Sun-spot Frequency is — 



A = A' + rA" 

 where r = Sun-spot Frequency. 



In applying Wolf's formula to the above observations A is taken 

 as the excess of the hourly mean over the monthly mean in minutes 

 «of arc (one sc. div. = -751'). 



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